A bunch of flies are trapped in a sealed jar. You place the jar on a set of scales. The scales will register the greatest weight when the flies are:
a) Sitting on the bottom of the jar
b) Flying around the inside of the jar
c) Neither; the weight is exactly the same in each case

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c) Neither.
The weight depends on the mass of the jar (including flies) and the position of the flies does not change that. Their weight in flight is transmitted to the bottom of the jar by the air currents generated by their wings.